PBT

Examples:
:pbt :max ; print back through the most recent command
:pbt :x ; print back through the most recent command
:pbt fn ; print back through the introduction of fn
:pbt 5 ; print back through the fifth command executed
:pbt (:x -4) ; print back through the most recent five commands

Pbt takes one argument, a command descriptor, and prints the
commands from :max (aka :x) through the one described.
See command-descriptor for a description of what a command
descriptor is. See pc for a description of the format used to
display commands. Pbt will print the commands that ubt will
undo.